Science 10: Unit 1 - Chemistry

Chapter 3

Chemical Vs. Physical Change

Chemical Change:

- Something new is made

- Chemical composition is affected

- Energy is absorbed(endothermic) or released

- A change in energy (light, sound, or electricity is released)

- Odor changes

- Bubbles/ precipitate forms

Physical Change:

- Change in state

- Nothing new is made

Endothermic Vs. Exothermic Reactions:

Endothermic: More energy is absorbed to break bonds than is released, so the environment LOSES energy (gets colder)

Exothermic: More energy is released than the energy taken to break the bonds, so the environment GAINS energy (gets hotter)

Different Types of Reactions:

Formation: Two elements combined into a compound (A + B = AB)

Na + Cl > NaCl

Decomposition: A compound separates into two elements (AB = A + B)

MgO > Mg + O

Single Replacement: An element replaces a similar element in a compound (AB + C = AC + B)

Mg(s) + Cu(NO3) > Mg(NO3) + Cu

Double Replacement: The negative and positive ions in a reaction (AB + CD > AC + BD)

KI + Pb(NO3) > KNO3 + PbI2

Combustion: A reaction that results in the release of oxygen gas and energy in the form of light and heat (A + O2 > CO2 + H2O)

The Law of Conservation of Mass and Balancing Equations:

Reactant + Reactant > Product

(Reactants create products in a chemical reaction. The arrow always points to the product)

The Law of Conservation of Mass states that the mass of the reactants must be equal to the mass of the product. In a closed system, no extra gas or substances can escape. In an open system, extra substances can escape. We assume chemical reactions take place in a closed system.

H2 + O2 > H2O

This is a skeleton equation. While it does make sense, it doesn't take into account the Law of Conservation of Mass. To make the equation balanced, we need to have the same number of atoms on both sides of the equation.

H2 + O2 > H2O

H = 2 | H = 2

O = 2 | O = 1

As we can see here, there is not an equal number of oxygen atoms on either side of the equation. So, we have to multiply the number of atoms we have on either side of the equation to make it equal.

2(H2) + (O2) > 2(H2O)

H = 4 (2x2) | H = 4 (2x2)

O = 2 | O = 2 (2x1)

We indicate what number we multiplied by with a larger number in front of the chemicals, called a subscript. Sometimes it can take multiple steps to balance an equation. In combustion equations, you have to go in this order (Carbon > Hydrogen > Oxygen) to balance the equation. For example:

CO2 + H2O > C6H12O6 + O2

This is the chemical formula for photosynthesis.

6(CO2) + 6(H2O) > C6H12O6 + 6(O2)

C = 6 (6x1) | C = 6

H = 12 (6x2) | H = 12

O = 18 (6x2) + (6x1) | O = 18 (6x2) + 6

While it was a little complicated, I managed to get it done! Now, how do we determine what state each molecule is in? We look at the solubility table!

If you look below, you can tell which elements are soluble in an ion. If something is soluble, it will be whatever state it is at room temperature. If it is not soluble, it will be solid. In our case, C6H12O6 is solid because it is sugar.

	Created by Riley Babuik over 5 years ago

Grade 8 Science Note on Science 10: Unit 1 - Chemistry, created by Riley Babuik on 06/09/2021.